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Journal of Energy Technologies and Policy www.iiste.org

ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online)

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Voltage Dip mitigation in Distribution System by Using D-

Statcom

Sambugari Anil Kumar1*

, D. vanurrappa2

1. Department of Electrical and Electronics Engineering, G.Pulla Reddy Engineering College,Kurnool-518007, Andhra Pradesh. India

2. Department of Electrical and Electronics Engineering, Brindavan Institute of Technology &Science,Kurnool -518218, Andhra Pradesh, India

* E-mail: [email protected]

Abstract

A Power quality problem is an occurrence manifested as a nonstandard voltage, current or

frequency that results in a failure or a mis-operation of end user equipments. Utility distribution networks,

sensitive industrial loads and critical commercial operations suffer from various types of outages and

service interruptions which can cost significant financial losses. With the restructuring of power systems

and with shifting trend towards distributed and dispersed generation, the issue of power quality is going to

take newer dimensions. In developing countries like India, where the variation of power frequency and

many such other determinants of power quality are themselves a serious question, it is very vital to take

positive steps in this direction .The present work is to identify the prominent concerns in this area and

hence the measures that can enhance the quality of the power are recommended.

This work describes the techniques of correcting the supply voltage sag, swell and interruption ina distributed system. At present, a wide range of very flexible controllers, which capitalize on newly

available power electronics components, are emerging for custom power applications. Among these, the

distribution static compensator and the dynamic voltage restorer are most effective devices, both of them

based on the VSC principle. A D-STATCOM injects a current into the system to correct the voltage sag,

swell and interruption. Comprehensive results are presented to assess the performance of each device as a

potential custom power solution

The STATCOM is applied to regulate transmission voltage to allow greater power flow in a voltage

limited transmission network, in the same manner as a static var compensator (SVC), the STATCOM has

further potential by giving an inherently faster response and greater output to a system with depressed

voltage and offers improved quality of supply. The main applications of the STATCOM are; Distribution

STATCOM (D-STATCOM) exhibits high speed control of reactive power to provide voltage stabilization

and other type of system control. The DSTATCOM protects the utility transmission or distribution system

from voltage sag and /or flicker caused by rapidly varying reactive current demand. During the transient

conditions the D-STATCOM provides leading or lagging reactive power to active system stability, power

factor correction and load balancing

Keywords: Distribution Static Synchronous Compensator (D-STATCOM), Voltage Dip, Distribution

System

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1. Introduction

One of the most common power quality problems today is voltage dips. A voltage dip is a short time (10 ms

to 1 minute) event during which a reduction in r.m.s voltage magnitude occurs. It is often set only by two

parameters, depth/magnitude and duration. The voltage dip magnitude is ranged from 10% to 90% of

nominal voltage (which corresponds to 90% to 10% remaining voltage) and with a duration from half a

cycle to 1 min. In a three-phase system a voltage dip is by nature a three-phase phenomenon, which affects

both the phase-to-ground and phase-to-phase voltages. A voltage dip is caused by a fault in the utility

system, a fault within the customers facility or a large increase of the load current, like starting a motor or

transformer energizing. Typical faults are single-phase or multiple-phase short circuits, which leads to high

currents. The high current results in a voltage drop over the network impedance. At the fault location the

voltage in the faulted phases drops close to zero, whereas in the non-faulted phases it remains more or less

unchanged.

Electric power distribution network becomes more increasingly important and plays an essential

role in power system planning. This type of power systems has a major function to serve distributed

customer loads along a feeder line; therefore under competitive environment of electricity market eservice

of electric energy transfer must not be interrupted and at the same time there must provide reliable, stable

and high quality of electric power. To complete this challenge, it requires careful design for power network

Planning. There exist many different ways to do so. However, one might consider an additional device to be

installed somewhere in the network. Such devices are one of capacitor bank, shunt reactor, series reactors,

and automatic voltage regulators and/or recently developed dynamic voltage restorers, distribution

STATCOM or combination of them.

Most industries and companies prefer electrical energy with high quality. If delivered energy to

these loads has poor quality, products and equipment of these loads such as microcontrollers, computers,

motor drives etc are damaged. Hurt of this phenomenon in companies that dealing with information

technology systems is serious. According to a study in U.S., total damage by voltage sag amounts to 400

Billion Dollars .For these reasons power quality mitigation in power systems is necessary. Nowadays,Custom Power equipments are used for this purpose. DSTATCOM is one of these equipments which can be

installed in parallel with. Sensitive loads. This device mitigates the load voltage by Injecting necessary

current to the system

2. Structure of Statcom

Basically, STATCOM is comprised of three main parts ,a voltage source inverter (VSI), a step-up coupling

transformer, and a controller. In a very-high-voltage system, the leakage inductances of the step-up power

transformers can function as coupling reactors. The main purpose of the coupling inductors is to filter out

the current harmonic components that are generated mainly by the pulsating output voltage of the power

converters.

2.1Voltage Source Converter (VSC)

A voltage-source converter is a power electronic device, which can generate a sinusoidal voltage with any

required magnitude, frequency and phase angle. Voltage source converters are widely used in adjustable-

speed drives, but can also be used to mitigate voltage dips. The VSC is used to either completely replace

the voltage or to inject the missing voltage. The missing voltage is the difference between the nominal

voltage and the actual. The converter is normally based on some kind of energy storage, which will supply

the converter with a DC voltage. The solid-state electronics in the converter is then switched to get the

desired output voltage. Normally the VSC is not only used for voltage dip mitigation, but also for other

power quality issues, e.g. flicker and harmonics.

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2.2 AControllerThe aim of the control scheme is to maintain constant voltage magnitude at the point where a sensitive load

is connected, under system disturbances. The control system only measures the r.m.s voltage at the load

point, i.e., no reactive power measurements are required. The VSC switching strategy is based on a

sinusoidal PWM technique which offers simplicity and good response. Since custom power is a relatively

low-power application, PWM methods offer a more flexible option than the Fundamental Frequency

Switching (FFS) methods favored in FACTS applications. Besides, high switching frequencies can be used

to improve on the efficiency of the converter, without incurring significant switching losses.

The controller input is an error signal obtained from the reference voltage and the value rms of the terminal

voltage measured. Such error is processed by a PI controller the output is the angle , which is provided to

the PWM signal generator. It is important to note that in this case, indirectly controlled converter, there is

active and reactive power exchange with the network simultaneously: an error signal is obtained by

comparing the reference voltage with the rms voltage measured at the load point. The PI controller process

the error signal generates the required angle to drive the error to zero, i.e., the load rms voltage is brought

back to the reference.

Pref

QrefAC

enery storage

controller)sin( = tvv m

v

P

Q

COUPLINGTRANSFORME

R

P

Fig.1Block diagram representation of STATCOM

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Fig.2 Single-line Diagram of a STATCOM and Its Control System Block Diagram

The control system consists of:

A phase-locked loop (PLL) which synchronizes on the positive-sequence component of the three-phase primary voltage V1. The output of the PLL (angle =t) is used to compute the direct-axis

and quadrature-axis components of the AC three-phase voltage and currents (labeled as Vd, Vq or

Id, Iq on the diagram).

Measurement systems measuring the d and q components of AC positive-sequence voltage andcurrents to be controlled as well as the DC voltage Vdc.

An outer regulation loop consisting of an AC voltage regulator and a DC voltage regulator. Theoutput of the AC voltage regulator is the reference current Iqref for the current regulator (Iq =

current in quadrature with voltage which controls reactive power flow). The output of the DC

voltage regulator is the reference current Idref for the current regulator (Id = current in phase with

voltage which controls active power flow).

An inner current regulation loop consisting of a current regulator. The current regulator controlsthe magnitude and phase of the voltage generated by the PWM converter (V2d V2q) from the

Idref and Iqref reference currents produced respectively by the DC voltage regulator and the AC

voltage regulator (in voltage control mode). The current regulator is assisted by a feed forward

type regulator which predicts the V2 voltage output (V2d V2q) from the V1 measurement (V1d

V1q) and the transformer leakage reactance.

3. Principle of Operation

The D-STATCOM is a three phase and shunt connected power electronics based reactive power

Compensation equipment, which generates and /or absorbs the reactive power whose output can be varied

so as to maintain control of specific parameters of the electric power system.

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The AC voltage difference across the leakage reactance power exchange between the D-STATCOM

and the Power system, such that the AC voltages at the busbar can be regulated to improve the voltage

profile of the power system, which is primary duty of the D-STATCOM.The D-STATCOM employs aninverter to convert the DC link voltage Vdc on the capacitor to a voltage source of adjustable magnitude

and phase. Therefore the D-STATCOM can be treated as a voltage controlled source. The D-STATCOM

can also be seen as a current controlled source. The basic objective of a VSI is to produce a sinusoidal AC

voltage with minimal harmonic distortion from a DC voltage. The operation of the D-STATCOM is as

follows: The voltage is compared with the AC bus voltage system (Vs).

When the AC bus voltage magnitude is above that of the VSI magnitude (Vc); the ACsystem sees the D-STATCOM as inductance connected to its terminals.

Otherwise if the VSI voltage magnitude is above that of the AC bus voltage magnitude, theAC system sees the D-STATCOM as capacitance to its terminals.

If the voltage magnitudes are equal, the reactive power exchange is zero.

If the D-STATCOM has a DC source or energy storage device on its DC side, it can supply real

power to the power system. This can be achieved by adjusting the phase angle of the D-STATCOM

terminals and the phase angle of the AC power system. When phase angle of the AC power system leads

the VSI phase angle, the DSTATCOM absorbs the real power from the AC system, if the phase angle of the

AC power system lags the VSI phase angle, the D-STATCOM supplies real power to AC system

Fig.3 Operating Principle of the STATCOM

4. Compensation schemes

4.1 General Compensation Scheme

A shunt-connected solid-state synchronous voltage source, composed of a six-pulse/five level, voltage-

sourced inverter and a dc energy storage device, is shown schematically in Figure 7. As explained in the

previous section, it can be considered as a perfect sinusoidal synchronous voltage source behind a coupling

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reactance provided by the leakage inductance of the coupling transformer. If the energy storage is of

suitable rating, the STATCOM can exchange both reactive and real power with the ac system. The reactive

and real power, generated or absorbed by the STATCOM, can be controlled independently of each other,and any combination of real power generation/absorption With var generation/absorption is possible, as

illustrated in Figure 7b. The real power that the STATCOM exchanges at its ac terminals with the ac system

must, of course, be supplied to, or absorbed from, its dc terminals by the energy storage device. By

contrast, the reactive power exchanged is internally generated by the STATCOM, without the dc energy

storage device playing any significant part in it.

Fig 4: a) shunt connected synchronous voltage source and b) its possible operating modes for real and

reactive power generation

4.2 Reactive Power Compensation Scheme

If the D-STATCOM is used only for reactive shunt compensation, like a conventional static var

compensator, then the dc energy storage device can be replaced by a relatively small dc capacitor. In this

case, the steady-state power exchange between the STATCOM and the ac system can only be reactive.

When the STATCOM is used for reactive power generation, the inverter itself can keep the capacitor

charged to the required voltage level. This is accomplished by making the output voltages of the inverter

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lag the system voltages by a small angle. In this way the inverter absorbs a small amount of real power

from the ac system to replenish its internal losses and keep the capacitor voltage at the desired level. The

same control mechanism can be used to increase or decrease dc capacitor voltage, and thereby theamplitude of the output voltage of the inverter, for the purpose of controlling the var generation or

absorption

Fig 5.a) synchronous voltage source operated as the static condenser b) its possible operating mode for

reactive power generation

5. Simulation Block Diagram of D-Statcom

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6. Simulation Results

6.1 Without D-Statcom

Here initially the D-STATCOM was not connected to the system and the load of three phase RLC load

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of 3MW, 0.2 MVAR is applied on the system in the time interval of 0.1sec to 0.5 sec. the voltage got

dipped from 1.12 p.u to 0.98p.u for voltage across B1 and 1.06 p.u to 0.94 p.u for voltage across B3.

6.2 With D-Statcom

Here the D-STATCOM was connected to the system and the load of three phase RLC load of 3MW,

0.2 MVAR is applied on the system in the time interval of 0.1sec to 0.5 sec. the voltage got dipped from

1.09 p.u to 1.01p.u for voltage across B1 and 1.02 p.u to 0.96 p.u for voltage across B3

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7. Conclusion

Voltage dip and voltage flickering are the two major power quality problems which are frequently seen in

the distribution systems. These power quality problems in 25KV, 100 MVA distribution system are

investigated in this paper. The analysis and simulation of a DSTATCOM application for the mitigation of

power quality problems are presented and discussed. The Mat lab Power System Block set simulation

results shows that the mitigation of the power quality problems (voltage dip and the voltage flickering)

done effectively with D-STATCOM.The voltage got dipped from 1.12 p.u to 0.98p.u for voltage across B1and 1.06 p.u to 0.94 p.u for voltage across B3 for without D-Statcom and 1.09 p.u to 1.01p.u for voltage

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across B1 and 1.02 p.u to 0.96 p.u for voltage across B3 with D-Statcom.

References

G.Yaleinkaya, M.H.J. Bollen, P.A. Crossley (1999), Characterization of voltage sags in industrial

distribution systems, IEEE transactions on industry applications, vol.34, no. 4, July/August, pp. 682-688.

Hague, M.H (2001), Compensation of distribution system voltage sag by DVR and D-STATCOM,

Power Tech Proceedings, 2001 IEEE Porto, vol.1, pp.10-13, Sept.

Peter Ashmole and Paul Amante (1997), System Flicker Disturbances from Industrial Loads and Their

Compensation, Power Engineering Journal, pp. 213-218, Oct.

W. N. Chang, C. J. Wu, and S. S. Yen (1998), A Flexible Voltage Flicker Teaching Facility for Electric

Power Quality Education, IEEE Trans.Power Systems, vol. 13, pp. 27-33, Feb.

M. K. Walker (1979), Electric Utility Flicker Limitations, IEEE Trans.Industrial Applications, vol. 15,

pp. 644-655, Nov.

Laszlo Gyugyi (1994), Dynamic compensation of ac transmission lines by solid-state synchronous voltage

sources IEEE transactions on power delivery, vol.9, no.2, pp.904-911, April.

Pirre giroux, G.sybille, Hoang le-huy (2001),Modeling and simulation of a D-STATCOM using

simulinks power system blockset The 27th annual conference of the IEEE industrial electronics society,

pp990-994.

Anaya-Lara O, Acha E (2002), Modeling and analysis of custom power systems by PSCAD/EMTDC,

IEEE Transactions on Power Delivery, Vol.17, and Issue: 1, Jan., Pages: 266 272.

R.Mienski, R.Pawelek and I.Wasiak (2004), Shunt Compensation for Power Quality Improvement Using

a STATCOM controller: Modeling and Simulation, IEEE Proce., Vol.151, No.2, March

S.Anil Kumar was born in India in 1986. He received his B.Tech in Electrical & Electronics Engineering

from Jawaharlal Nehru Technological University, Hyderabad in 2007. He is pursuing his Master ofTechnology in Electrical power systems from the Jawaharlal Nehru Technological University, Anantapur.

He is currently working as an Assistant Professor in Electrical and Electronics Engineering Department at

G.Pulla Reddy Engineering College, Kurnool. His Research interests include electric power distribution

systems, HVDC, FACTS and Power system operation and control.

D.Vanurrappa was born in India in 1982. He received his B.Tech in Electrical & Electronics Engineering

from Jawaharlal Nehru Technological University, Hyderabad in 2007. He is pursuing his Master of

Technology in Electrical power systems from the Jawaharlal Nehru Technological University, Anantapur.

He is currently working as an Assistant Professor in Electrical and Electronics Engineering Department at

Brindavan Institute of Technology & Sciences, Kurnool. His Research interests include electric power

distribution systems, HVDC, FACTS and Power system operation and control.

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